Monday, 16 July 2007

Performance Part IV

Next on the performance hitlist is port tracking. This one is slightly more tricky to collect in Tuning Manager as HTnM uses absolute values for port throughput (Port IOPS and Port Transfer) in alerting, rather than relative values like % busy. This is a problem because the figures of both IOPS and throughput (KB/MB/s) will vary wildly depending on the traffic profile.

For instance, a high number of very small blocksize I/O will overwhelm the processor managing the port (resulting an seemingly low throughput) however a large blocksize could max out the storage port in terms of throughput (i.e. pushing a 2Gb/s FC link to its limit). As processor busy isn't available for alerting either, then I'd set a threshold limit on Port Transfer based on the capacity of the fibre channel interface. For example, with a 2Gb/s port, throughput should never be over 50% (if you want 100% redundancy in case of path loss) so I'd set figures of 40% of capacity for warning and 50% for critical in HTnM alerting. That's 40MB/s and 100MB/s respectively. These are high figures and sustained throughput at this level may require some load balancing or attention. If these levels generate no alerting then it may be possible to reduce them to start highlighting peaks.

Choosing a figure for IOPS is more problematic. I'd suggest picking an arbitrary level based on a few week's data from all ports. Set a limit based on historical data that's likely to trigger the occasional altert but will not create critical errors continually. Alerts can then be monitored and if there are alert trends, action can be taken. Hopefully it should be then possible to start to reduce alerting thresholds as more issues are solved.

Although TrueCopy initiators can't be monitored, RCU Targets can, so the same logic can be applied to throughput values.

On a totally unrelated subject, I have a recommendation to never de-seed chillis without gloves. I've just removed the seeds from my first crop of the year (including the wonderful looking purple tiger) and my entire face is glowing where I've wiped it. I have no idea how I'm now going to get my contact lenses out...

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